Inlet valves of an ABS or ESP system are typically operated either in a so-called switching mode or in a so-called (pressure difference) setting mode. In this case, the switching mode is characterized by brief full strokes and the (pressure difference) setting mode by volumetric flow-dependent partial strokes.
In the switching mode, the inlet valve opens fully and enables the maximum possible flow through the valve, which essentially depends on the pressure difference arising across the valve. The switching mode is robust in terms of the reproducibility thereof, in particular against fluctuating boundary conditions, and is highly dynamic and typically only very short-term, in particular being active for a few milliseconds or for the selected operating mode.
In the (pressure difference) setting mode, the inlet valve only opens in partial strokes according to the selection of the electric current, and as a result enables significantly smaller flows, i.e. volumetric flows. In the setting mode, typically pressure difference-dependent and regularly also valve-specific deviations occur between the actual and target values. In specific driving situations, said deviations can be greater than in the switching mode.
Therefore, the switching mode for inlet valves for driving safety systems has become established for such special driving situations, whereas in many other application areas, in particular on snow and ice, the (pressure difference) setting mode is used. One disadvantage of the switching mode however, is that in the switching mode comparatively loud valve closure noise arises, which is due to the so-called “water hammer” when suddenly decelerating the accelerated column of fluid. If fluids with high elasticity are used in connection with driving safety systems, then said (noise) problem increases further, because in this case large throughflows or large volumetric flows pass through the valve and must be controlled by the valve.
An (idealized) example of a flow profile, with which the valve can be actuated in the switching mode, is shown schematically in FIG. 1 together with an (idealized) valve position profile, which is set because of the actuation of the valve with the same current profile. The current profile 4 is shown in the upper part of FIG. 1 and the associated valve position profile 5 is shown in the lower part of FIG. 1. Using the profile of the valve position 7, it can be seen that the valve is operated only with full strokes 8 in the switching mode. But when closing the valve this results in a sudden deceleration of the accelerated column of fluid and so-called “water hammer” occurs, resulting in increased noise generation. The decisive position of the valve position profile 5 is highlighted in FIG. 1 with an elliptical border.